Biol116 Lecture #8 (10/15/25) (In class)

Demography

the study of population or populations with reference to size, density, fertility, mortality, growth, age distribution, and migration.

(populations) fluctuations

random and cyclic changes through time

Factors for fluctuations

• Availability of resources

• predation

• competition

• disease

• parasites

• climates

Other populations exhibit much _____

wider fluctuations

Overshoot

a population grows beyond its carrying capacity

• often occurs when the carrying capacity of the habitat decreases from one year to the next (less resources)

Die off

a substantial decline in density that typically goes well below the carrying capacity.

(population goes below the carrying capacity)

Population cycles

Regulat oscillation of a population over a longer period of time

Which populations are more vulnerable to extinction (Small or large)

Small

Extinction probability

of birds on the Channel Islands is inversely correlated with population size

Preferred habitats often occur as patches of ___ habitat surrounded by ___ habitat

suitable, unsuitable

example: aquatic organisms

Fragmented habitats

Sources

Sinks

Sources

high quality patches that produce a large number of individuals that disperse to other patches

Sinks

Low quality patches that produce few individuals and rely on dispersers t keep the sink population from going extinct